It is desirable to provide enclosures for mechanical devices, such as fans, switches, compressors and other devices, to suppress vibration and sound associated with the operation of the device.
Holub et al, U.S. Pat. No. 4,122,061 describes polyester reinforced blends of poly(1,4-butylene terephthalate) and poly(ethylene terephthalate) impact modified with the addition of a polyolefin or olefin based copolymer resin. The polyolefinic resin is dispersed into the polyester blend and used for injection molding. Workpieces molded from such polyester resins are described as having a high degree of surface hardness and abrasion resistance, high gloss, and lower surface friction. It is desirable to provide further enhancements to the properties of resins of the type described in Holub et al.
U.S. Pat. No. 5,441,997 describes polyester molding compositions which have ceramic like qualities, can be molded into relatively thin sections, and have high impact strength. The composition is directed to a polybutylene terephthalate and/or polyethylene terephthalate and an aromatic polycarbonate with inorganic fillers selected from the group consisting of barium sulfate, strontium sulfate, zirconium oxide and zinc sulfate. If desired, a styrene rubber impact modifier is described as an added ingredient to the composition as well as a fibrous glass reinforcing filler. Although these compositions are suited for applications where ceramic like qualities are desired, compositions having additional enhanced properties are desirable.
Various rubbery modifiers have been added to polyesters to improve impact. U.S. Pat. No. 4,022,748 discloses rubber elastic graft copolymers having a glass transition below -20.degree. C. U.S. Pat. No. 4,034,013 and 4,092,202 disclose multistage polymers having a rubbery interior and a hard outer shell preferably derived from acrylates. U.S. Pat. No. 4,090,966 and 4,271,064 disclose selectively hydrogenated monoalkenyl arene-diene block copolymers as polyester modifiers. U.S. Pat. No. 4,257,937 describes polyester polycarbonate blends with polyacrylate resins. A wide variety of other polyester impact modifiers have been disclosed in the art, but none address the issue of sound and vibration damping along with retention of a good balance of mechanical and rheological properties.
Vibration damping has been addressed through the use of specific styrenic block copolymers in other thermoplastics such as ethylene-polypropylene as described in Jpn. Kokai Tokkyo Koho JP11 80,456[99 804561]: (Chem Abstracts 130: 238309). U.S. Pat. No. 5,886,094 discloses an inorganic filler with a compatibilizer and styrene block copolymer; in a polyphenylene ether polyamide mixture to increase damping.
Despite all prior work combining thermoplastic polyesters and rubbery impact modifiers there still remains the need to provide a crystalline thermoplastic polyester with high heat, solvent resistance and good mechanical and rheological properties having the additional characteristic of sound and vibration damping.